(1) Field of Invention
The present invention relates to a process used for fabrication of SiC and AlN on diamond or diamond-like carbon (DLC) wafers, and more particularly, SiC and AlN on wafers that can be used as substrates for deposition of GaN Heterojunction Field Effect Transistors (HFETs).
(2) Discussion of Related Art
All systems that use high-power microwave and millimeter-wave power sources utilize GaN Heterojunction Field Effect Transistors (HFETs). The power performance of GaN HFETs are currently limited by the thermal management of the device. The efficiency with which heat is dissipated from the device is ultimately limited by the thermal conductance of a substrate material. SiC, currently the substrate material of choice for deposition of GaN HFET epi-layers, is an excellent thermal conductor. However, the thermal conductance of SiC (i.e., 4.5 W/mm) is still substantially lower than that of the best known thermal conductor, diamond. AlN, which is another substrate suitable for deposition of GaN HFETs, has an even poorer thermal conductance (i.e., 3.3 W/mm) than SiC.
From the standpoint of thermal management, diamond would be an ideal substrate for fabrication of high power GaN HFETs, as it would provide higher output power densities than current devices fabricated on SiC. The current technique for deposition of large diameter diamond films, Plasma Enhanced Chemical Vapor Deposition (PECVD), produces only polycrystalline diamond films. However, polycrystalline diamond films alone are not suitable for deposition of single-crystal films that are required for fabrication of electron devices.
Thus, a continuing need exists for a fabrication process that forms a diamond, or diamond-like substrate for fabrication of high power GaN HFETs.